Reaction apparatus for producing silicon

ABSTRACT

A silicon production reactor comprising a reaction vessel and heating means, said reaction vessel comprising a vertically extending wall and a space surrounded by the wall, said heating means being capable of heating at least a part, including lower end portion, of the wall&#39;s surface facing the space to a temperature of not lower than the melting point of silicon, said silicon production reactor being adapted to flow raw gas for silicon deposition from an upper part of the space of the reaction vessel toward a lower part thereof, characterized in that the space of the reaction vessel is of slit form in cross-sectional view. This silicon production reactor is capable of attaining improvement with respect to problems encountered at apparatus scaleup, such as decrease of reactivity of raw gas and generation of by-products, thereby accomplishing a striking enhancement of production efficiency.

TECHNICAL FIELD

The present invention relates to a novel silicon production reactor.More particularly, the present invention relates to a silicon productionreactor that in the industrial production of silicon continuouslyperformed for a prolonged period of time, is capable of enhancing thereactivity of raw gas and capable of suppressing the generation ofby-products to thereby maintain a high silicon yield and attain anenhancement of production efficiency.

BACKGROUND ART

In the art, various processes for producing silicon for use as a rawmaterial for semiconductors and photocells are known. Some thereof arealready put into industrial practice.

For example, there can be mentioned the process known as Siemensprocess. In the Siemens process, a silicon rod having been heated tosilicon deposition temperature by current passage is disposed in a belljar, and trichlorosilane (SiHCl₃, hereinafter referred to as TCS) ormonosilane (SiH₄) together with a reducing gas such as hydrogen isbrought into contact with the heated silicon rod to thereby performdeposition of silicon.

This process is characterized in that a high-purity silicon can beobtained, and carried out as the most common process. However,deposition is performed batchwise, so that there is such a problem thatan extremely complex procedure including arranging of a silicon rod asseed, heating of the silicon rod by current passage, deposition,cooling, takeout, bell jar cleaning, etc. is inevitable.

With a view toward resolving this problem, Japanese Patent Laid-openPublication No. 2002-29726 proposes a silicon production reactor capableof producing silicon stably and continuously over a prolonged period oftime. In this silicon production reactor, while feeding a raw gas forsilicon deposition into a tubular vessel capable of being heated to atemperature of not lower than the melting point of silicon, the tubularvessel is heated so as to perform deposition of silicon. The depositedsilicon is continuously melted and caused to fall from the lower end ofthe tubular vessel, thereby attaining collection of silicon.

This reactor is a very excellent apparatus capable of resolving variousproblems of the conventional Siemens process and capable of continuousproduction of silicon. However, when a scaleup of the reaction vessel ofcylindrical configuration, etc. described in Examples of Japanese PatentLaid-open Publication No. 2002-29726 is performed as it is with anintent to produce silicon on an industrial scale of hundreds of tons ormore per year, the reactivity of raw gas would inevitably drop. Further,fine powder of silicon and by-products such as low-molecular-weightpolymers of silane compounds are likely to be generated, thereby tendingto invite a decrease of silicon yield. In these respects, an improvementhas been demanded.

DISCLOSURE OF THE INVENTION

The inventors have made extensive and intensive studies with a viewtoward resolving the above problems. As a result, it has been found thatin the above apparatus, the above problems are caused by theconfiguration in cross-sectional view of the inside face of the tubularvessel. That is, when a scaleup of a reactor wherein the inside face ofthe tubular vessel has the shape of simple circle, regular polygon orthe like in cross-sectional view is carried out, there would be a spacehighly apart from the heated inside face of the tubular vessel, therebyinviting problems such as decrease of raw gas reactivity and tendencytoward by-product formation. Studies have been conducted on the basis ofthis finding. As a result, it has been found that all the above problemscan be solved by a reaction vessel comprising a vertically extendingwall and a space surrounded by the wall wherein the space of thereaction vessel is of slit form in cross-sectional view so as to reducethe space highly apart from the wall's surface facing the space, namely,shortening the distance between the wall's surface capable of silicondeposition and the space where raw gas therein hardly contact with thewall's surface. The present invention has been completed on the basis ofthis finding.

Thus, according to the present invention, there is provided a siliconproduction reactor comprising a reaction vessel and heating means, saidreaction vessel comprising a vertically extending wall and a spacesurrounded by the wall, said heating means being capable of heating atleast a part, including lower end portion, of the wall's surface facingthe space to at temperature of not lower than the melting point ofsilicon, said silicon production reactor being adapted to flow raw gasfor silicon deposition from an upper part of the space of the reactionvessel toward a lower part thereof, characterized in that the space ofthe reaction vessel is of slit form in cross-sectional view.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of portion of a fundamental form of siliconproduction reactor according to the present invention, which view showsa vertical section of the reactor.

FIG. 2 is a schematic view of portion of another fundamental form ofsilicon production reactor according to the present invention, whichview shows a vertical section of the reactor.

FIG. 3 is a schematic view of portion of a further fundamental form ofsilicon production reactor according to the present invention, whichview shows a vertical section of the reactor.

FIG. 4 is a schematic view of portion of a representative practical formof silicon production reactor according to the present invention, whichview shows a vertical section of the reactor.

FIG. 5 is a cross-sectional view of a representative space surrounded bya vertically extending wall in a silicon production reactor of thepresent invention.

FIG. 6 is a cross-sectional view of another representative spacesurrounded by a vertically extending wall in a silicon productionreactor of the present invention.

FIG. 7 is a cross-sectional view of a further representative spacesurrounded by a vertically extending wall in a silicon productionreactor of the present invention.

FIG. 8 is a cross-sectional view of still a further representative spacesurrounded by a vertically extending wall in a silicon productionreactor of the present invention.

FIG. 9 is a cross-sectional view of yet still a further representativespace surrounded by a vertically extending wall in a silicon productionreactor of the present invention.

-   1: reaction vessel,-   2: opening,-   3: heating means,-   3′: heating means,-   4: space,-   5: raw gas supply pipe,-   6: raw gas blowoff port,-   7: cooling means,-   8: seal gas supply pipe,-   9: waste gas discharge pipe,-   10: sealed vessel,-   11: seal gas supply pipe,-   12: cooling gas supply pipe,-   13: cooling jacket,-   14: cooled space of sealed vessel,-   15: silicon,-   16: partition board,-   17: silicon take-out port,-   A: raw gas for silicon deposition,-   C: seal gas,-   I: reaction zone,-   a: wall, and-   a′: wall.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described below with reference to appendeddrawings showing representative embodiments thereof, which however in noway limit the scope of the present invention.

FIGS. 1 to 3 are schematic views of portion of a fundamental form ofsilicon production reactor according to the present invention. FIG. 4 isa schematic view of a representative practical form of siliconproduction reactor according to the present invention. (All FIGS. 1 to 3and FIG. 4 are views showing a vertical section of the reactor.) FIGS. 5to 9 are cross-sectional views of a space of representativeconfiguration surrounded by a vertically extending wall in a siliconproduction reactor of the present invention. For example, with respectto the silicon production reactor of FIGS. 1 and 3, configurations ofsection on the plane (E)-(E′) of the drawings are shown in FIGS. 7, 8and 9. Likewise, with respect to the reactor of FIG. 2, a configurationof section on the plane (E)-(E′) of the drawing is shown in FIG. 6.

One form of silicon production reactor according to the presentinvention will be described referring to FIG. 1. This silicon productionreactor is so structured that raw gas for silicon deposition (A)(hereinafter may be referred to as “raw gas”) is allowed to flow throughspace (4) surrounded by vertically extending wall (a) constitutingreaction vessel (1), and that silicon deposition/melting is performed ona heated surface of wall (a) facing the space (4) and molten silicon isallowed to fall through bottom opening (2).

In the silicon production reactor of the present invention, it isessentially important that the space (4) of the reaction vessel (1) beof slit form in cross-sectional view.

That is, in the silicon production reactor of the present invention, thespace highly apart from the heated surface of wall (a) facing the space(4) is reduced by causing the space (4) of the reaction vessel (1) to beof slit form in cross-sectional view. That is, the distance between thesurface of wall (a) and the space where raw gas therein hardly contactwith the surface of wall (a) is shortened to thereby enhance thereactivity of raw gas and inhibit the generation of by-products with theresult that a striking enhancement of silicon production efficiency canbe attained.

The effect exerted by the space (4) of the reaction vessel (1) being ofslit form in cross-sectional view according to the present inventionwill be described. As compared with a reactor of identical surface areawith respect to portion with which raw gas can be brought into contactwherein the space (4) of the reaction vessel (1) in cross-sectional viewhas width (SD) and length (LD) equal to each other, for example, iscircular, regular polygonal or the like, the reactor wherein the space(4) of the reaction vessel (1) in cross-sectional view is of slit formrealizes a reduction of the space highly apart from the heated surfaceof wall (a) facing the space (4). Thus, in the reactor wherein the space(4) of the reaction vessel (1) in cross-sectional view is of slit form,the probability of contact of raw gas with the wall's surface can beenhanced, so that the reactivity of raw gas can be enhanced. Further, asa result of easing of the contact of raw gas with the surface of wall(a), the temperature of raw gas in the space (4) can be satisfactorilyraised as a whole to thereby enable narrowing a temperature zone inwhich by-products are likely to be generated. Consequently, anenhancement of silicon yield can be realized.

Herein, the reactivity of raw gas is defined as the ratio of conversionfrom the raw gas fed into the space (4) of the reaction vessel (1) tosome other substances (including silicon) by the time of the dischargethereof from the space (4). The yield of silicon is defined as the ratioof the raw gas having been converted into silicon to the raw gas havingbeen converted into some other substances (including silicon) throughthe above reaction.

In the reaction conducted at the same gas feeding rate, when the space(4) of the reaction vessel (1) is of slit form in cross-sectional view,the flow-rate of raw gas is increased and thereby the residence time ofraw gas in the space (4) is shortened. However, within the residencetime of raw gas described later, the reactivity of raw gas does notdecrease despite the shortening of the residence time of raw gas. Thereason would be that in the silicon production reactor of the presentinvention, as compared with the conventional Siemens process, not onlycan deposition of silicon be accomplished at high surface temperaturefor deposition but also the raw gas can have its temperaturesatisfactorily raised and can be activated, so that there can be exertedthe effect of conversion to silicon attained within an extremely shortperiod of time upon contact of raw gas with the heated surface of wall(a) facing the space (4).

The effect exerted by the reactor wherein the space (4) of the reactionvessel (1) is of slit form in cross-sectional view according to thepresent invention will be studied in comparison with a reactor of thesame volume wherein the space (4) of the reaction vessel (1) incross-sectional view has width (SD) and length (LD) equal to each other,for example, is circular, regular polygonal or the like. In the reactionconducted at the same gas feeding rate, the residence time of raw gas inthe space (4) would be the same. However, when the space (4) of thereaction vessel (1) is of slit form in cross-sectional, the surface areaof portion capable of silicon deposition per gas feeding rate can beenlarged with the result that the reactivity of raw gas can be enhancedand that an effective productivity enhancement can be accomplishedwithout change in the scale of the reactor.

Moreover, in the scaleup of the reactor wherein the space (4) of thereaction vessel (1) is of slit form in cross-sectional view, there canbe realized not only the above effects but also the effect ofeffectively avoiding radiation heat loss at upper and lower end portionsof the heated surface of wall (a) facing the space (4) to thereby attaina drastic saving of heating energy. That is, in the use of the siliconproduction reactor of the present invention, the heated surface of wall(a) facing the space (4) can provide its intervening space narrowed tothereby reduce the area of opening of the reaction vessel. Accordingly,not only can outward radiation loss be drastically reduced but also thetemperature drop at upper and lower end portions of the surface can beeffectively inhibited with the result that a uniform temperaturedistribution over reaction zone can be realized with reduced heatingenergy. This effect is especially striking in embodiments of the presentinvention carried out at high temperatures of 1000° C. or higher whereinradiant energy is large.

In the present invention, the slit forms include those wherein the slithas a flattened shape or a shape of a ring being continuous in thecircumferential direction. The width of the slit form may be constant orinconstant or a combination thereof in the longitudinal direction of theslit form. Examples of the slit forms of constant width include anannular slit form as shown in FIG. 6, a slit form of rectangular shapeas shown in FIG. 9 and, not shown, a slit form of C-character shapecorresponding to curved rectangular shape. Examples of the slit forms ofinconstant width include an elliptic slit form as shown in FIG. 7 and,not shown, rhombic and triangular slit forms. Further, there can bementioned as a combination thereof a slit form of rectangular having itsfour corners arc-shaped as shown in FIG. 8. As other slit forms, therecan be mentioned a horseshoe-shaped slit form consisting of acombination of rectangles as shown in FIG. 5 and, not shown, L-charactershaped, T-character shaped, cross shaped and star shaped slit forms aswell as other curved and wave shaped slit forms.

With respect to the determination of width (SD) and length (LD) of slitforms described above, some illustrations are given in FIGS. 5 to 9. Thelength (LD) of slit generally refers to the largest distance along thelongitudinal direction within the slit. On the other hand, the width(SD) of slit is shorter than the length (LD) of the slit and when theslit form has a constant width, the width (SD) refers to the inter-walldistance. When the slit form has an inconstant width (SD) in thelongitudinal direction, the width (SD) is defined as the largest lengthof perpendicular line drawn to a line representing the longitudinaldirection (LD line) within the slit. On the other hand, when the slitform is inflected or curved, the length (LD) is defined as the length ofstraight or curving line which passes through the middle points ofsegments representing the smallest distance between wall portionsopposite to each other.

For example, in FIG. 5, the width (SD) refers to the inter-walldistance, and the length (LD) refers to the length of horseshoe-shapedline passing through the midpoints of wall portions opposite to eachother. Further, in the T-character shaped slit form as well, althoughnot shown, the width (SD) refers to the inter-wall distance, and thelength (LD) refers to the length of T-character shaped line passingthrough the midpoints of wall portions opposite to each other. Sameapplies to the cross shaped slit form.

In FIG. 6, the width (SD) refers to the distance between inside wall(a′) and outside wall (a). The length (LD) refers to the circumferenceof a circle passing through the midpoints between inside wall (a′) andoutside wall (a).

In FIG. 8, the width (SD) refers to the largest length of perpendicularline drawn to LD line within the slit. The length (LD) refers to thelargest distance along the longitudinal direction.

In FIG. 9, the width (SD) refers to the inter-wall distance. The length(LD) refers to the largest distance along the longitudinal direction.

When the shape in cross-sectional view of the reaction vessel iselliptic as shown in FIG. 7, the width (SD) refers to the minor axiswhile the length (LD) refers to the major axis.

In the rhombic slit form, although not shown, the width (SD) refers tothe smallest length of diagonal line. The length (LD) refers to thelargest length of diagonal line. Moreover, in the triangular slit form,the length (LD) refers to the longest side while the width (SD) refersto the distance between the longest side and the angle opposite thereto.

In the silicon production reactor of the present invention, it ispreferred that the ratio (LD/SD) of length (LD) to width (SD) of theslit form be 1.5 or higher. When the ratio (LD/SD) is below 1.5, theeffect of enhancing the reactivity of raw gas tends to be notconspicuous. On the other hand, the upper limit of ratio (LD/SD),although not particularly restricted, is preferably up to 1000 from theviewpoint of reactor fabrication. With respect to the slit form, takingthe above effect and reactor fabrication into account, there can bestated that the ratio (LD/SD) is more preferably in the range of 2 to400, still more preferably 3 to 300.

The width (SD) of slit form is preferably 0.1 m or less. When the width(SD) exceeds 0.1 m, the effect of enhancing the reactivity of raw gastends to be not conspicuous. On the other hand, the lower limit of width(SD), although not particularly restricted, is preferably at least 0.005m from the viewpoint of reactor fabrication. With respect to the slitform, taking the above effect and reactor fabrication into account, thewidth (SD) is more preferably in the range of 0.01 to 0.08 m, still morepreferably 0.01 to 0.06 m.

In connection with the relationship between length (LD) and width (SD)of slit form, it is preferred that the length (LD) of slit form be 0.15m or greater from the viewpoint of industrial production of silicon. Onthe other hand, the upper limit of length (LD), although notparticularly restricted, is preferably up to 5 m from the viewpoint ofreactor fabrication. Taking the quantity of silicon production andreactor fabrication into account, the length (LD) is more preferably inthe range of 0.16 to 4 m, still more preferably 0.18 to 3 m.

In the silicon production reactor of the present invention, theconfiguration in longitudinal sectional view of the space (4) of thereaction vessel (1), although not particularly restricted, can be ofcylindrical form as shown in FIGS. 1 to 3 with a view toward easing thefabrication thereof. Alternatively, it can be of form provided with ataper part such that its diameter is gradually decreased toward theopening (2).

With respect to the opening (2) provided at the bottom of the space (4)of the reaction vessel (1), the rim part thereof can be formed so as tobe horizontal without any problem in obtaining particulate silicon. Therim part can however also be formed so as to be sloped or waved.

Further, with respect to the configuration of the rim part of theopening (2), when silicon is collected as a melt, the rim part ispreferably formed into a blade shape having the thickness graduallydecreased toward the front edge in order to ensure satisfactory drainageat the fall of molten silicon from the wall (a).

In the silicon production reactor of the present invention, when thespace (4) of the reaction vessel (1) is of form with an inconstant widthin longitudinal sectional view as described above, the ratio of length(LD)/width (SD), width (SD) and length (LD) values of the slit formrefer to averages thereof over the region wherein the raw gas is broughtinto contact with the surface of wall (a) facing the space (4) tothereby realize silicon deposition (hereinafter may be referred to as“reaction zone (I)”). That is, the ratio of length (LD)/width (SD),width (SD) and length (LD) values of the slit form refer to averagesthereof over the space (4) extending from the uppermost edge to thelowermost edge of the reaction zone (I) shown in FIGS. 1 to 3.

When the raw gas blowoff port (6) is positioned above the uppermost edgeof heating means (3) as shown in FIGS. 1 and 2, the position of theuppermost edge of the reaction zone (I) is regarded as agreeing with theposition of the uppermost edge of the heating means (3). On the otherhand, when the position of the raw gas blowoff port (6) agrees with oris below the position of the uppermost edge of heating means (3) asshown in FIG. 3, the position of the uppermost edge of the reaction zone(I) is regarded as agreeing with the position of the raw gas blowoffport (6).

In the silicon production reactor of the present invention, with respectto the vertically extending wall (a) of the reaction vessel (1), it isessentially important to heat at least a part, including lower endportion, of the surface of wall (a) facing the space (4) to atemperature of not lower than the melting point of silicon. In thesurface of wall (a) facing the space (4), the region heated to atemperature of not lower than the melting point of silicon is notparticularly limited as long as the lower end portion is includedtherein, and can be appropriately determined in consideration of thefeed rate or speed of the raw gas etc. In this connection, it issatisfactory to take measures for heating the entirety of the wall'ssurface on which silicon deposition occurs (reaction zone (I)) to atemperature of not lower than the melting point of silicon. Accordingly,it is preferred that the region heated to a temperature of not lowerthan the melting point of silicon should be 90% or less, especially 80%or less of the whole length of vertically extending wall (a) from thebottom thereof, from the viewpoint that it is easy to prevent siliconscale attachment to the upper part of reaction vessel (1). For ensuringthe quantity of silicon produced, the lower limit of the region heatedto a temperature of not lower than the melting point of silicon is 20%or more, preferably 30% or more of the whole length of verticallyextending wall (a) from the bottom thereof.

In the silicon production reactor of the present invention, the raw gassupply pipe (5) is for flowing of raw gas from an upper part of thespace (4) of the reaction vessel (1) toward a lower part thereof.Referring to FIGS. 1 and 2, the position of the raw gas blowoff port (6)of the raw gas supply pipe (5) can be above the uppermost edge of theregion heated to a temperature of not lower than the melting point ofsilicon within the surface of wall (a) facing the space (4), namely, theuppermost edge of the reaction zone (I). Alternatively, referring toFIG. 3, the position of the raw gas blowoff port (6) can be equal to orbelow the position of the uppermost edge of the reaction zone (I).

In the present invention, when as shown in FIGS. 1 and 2, the positionof the raw gas blowoff port (6) of the raw gas supply pipe (5) is abovethe uppermost edge of the region heated to a temperature of not lowerthan the melting point of silicon within the surface of wall (a) facingthe space (4), namely, the uppermost edge of the reaction zone (I)), thequantity of heat deprived of by the raw gas supply pipe (5) can bereduced to thereby enhance the energy efficiency of heating means (3).In this structure, the method of silicon deposition/melting can be onecomprising setting the surface of wall (a) facing the space (4) withinthe reaction zone (I) at the temperature permitting silicon deposition,thereby performing silicon deposition once and resetting the abovesurface at the temperature of not lower the melting point of silicon soas to melt the deposited silicon and cause the molten silicon to fall.

In this method of silicon deposition/melting, with respect to means forcontrolling the heating means (3), it is preferred that the surface ofwall (a) facing the space (4) be divided into two sections consisting ofupper and lower sections, or more multiple sections so that temperaturecontrol can be conducted for individual sections. With respect toparticular means for controlling the heating means (3), preferably, theheating means (3) is divided into at least two sections consisting of afirst heating means mainly used during silicon deposition reaction and asecond heating means for heating area of the surface of wall (a) facingthe space (4) which is heated by heat transfer to bring about silicondeposition, each of the first and second heating means being capable ofregulation of heat output. Specifically, with respect to the secondheating means, the heat output is set at low level or zero duringsilicon deposition reaction. However, when melting deposited silicon,the heat output is increased to thereby cause silicon to fall. Thus, thegrowth of silicon scale within the reaction vessel (1) can be prevented.

In this method of silicon deposition/melting, as the method for removingany silicon scale attached to the inside of the reaction vessel (1),there can be employed not only the above method of controlling theheating means (3) but also the method of intermittently feeding anetching gas such as hydrogen chloride so as to remove any attachedscale. Also, a combination thereof can be employed.

In the present invention, when the position of the raw gas blowoff port(6) of the raw gas supply pipe (5) is equal to or below the uppermostedge of the reaction zone (I) as shown in FIG. 3, the method of silicondeposition/melting can be one comprising setting the surface of wall (a)facing the space (4) within the reaction zone (I) at the temperature ofnot lower than the melting point of silicon so as to perform continuousfall of silicon melt. Also, there can be employed the method comprisingsetting the above surface at the temperature permitting silicondeposition, thereby performing silicon deposition once and resetting theabove surface at the temperature of not lower than the melting point ofsilicon so as to melt the deposited silicon and cause the molten siliconto fall. In these methods, as described later, for preventingundesirable silicon deposition/growth in the interstice between thevertically extending wall (a) and the raw gas supply pipe (5) where is alow-temperature region that silicon may be deposited in solid form, itis preferred to feed a seal gas (seal gas (C), seal gas supply pipe (8)into the low-temperature region.

In these methods of silicon deposition/melting, the method ofcontrolling heating means (3) can be one comprising controlling theentirety of the wall's surface associated with silicon deposition at thesame temperature. Alternatively, the above surface can be divided intotwo sections consisting of upper and lower sections, or more multiplesections, and temperature control can be performed for each of thesections. The temperature control can be performed by single heatingmeans (3) of the reaction vessel (1), or can be performed by multipleheating means corresponding to each of the multiple sections.

In the silicon production reactor of the present invention, as theheating means (3), common means can be employed without any particularlimitation as long as the surface of wall (a) facing the space (4) canbe heated thereby to temperature of not lower than the melting point ofsilicon. It is considered that the melting point of silicon is in therange of 1410 to 1430° C. Specifically, as the heating means, there canbe mentioned those capable of heating the surface of wall (a) facing thespace (4) with the use of external energy. More specifically, there canbe mentioned those utilizing high-frequency heating, heating wire andinfrared heating.

Among them, the high-frequency heating means can preferably be usedbecause heating of the surface of wall (a) facing the space (4) touniform temperature can be easily accomplished with the configuration ofhigh-frequency emitting heating coil simplified.

Further, in the silicon production reactor of the present inventionusing the high-frequency heating means, a heat insulator can be insertedbetween the wall (a) and the heating means (3) in order to enhanceenergy efficiency of heating.

In the silicon production reactor of the present invention, foreffectively expanding the surface area of wall (a) associated withsilicon deposition relative to the scale of the reactor, it is preferredthat the space of the reaction vessel (1) be annular in cross-sectionalview as shown in FIG. 6. In this configuration, heating means (3′) asshown in FIGS. 2 and 6 can also be provided for satisfactorily heatingthe surface of inside wall (a′) facing the space (4).

As other heating means, there can be employed an embodiment wherein theoutside wall (a) is constituted of a 10 mm or less thickcarbon-fiber-reinforced carbon composite material while the inside wall(a′) is constituted of common isotropic carbon so that both the surfacesof outside wall (a) and the inside wall (a′) facing the space can besimultaneously heated by only the outside heating means (3) ofhigh-frequency etc. That is, the carbon-fiber-reinforced carboncomposite material constituting the outside wall (a) exhibit higherstrength to thereby enable thickness reduction of the wall (a) andexhibit lower electric conductivity as compared with those of commonisotropic carbon, so that high-frequency energy from the heating means(3) can appropriately penetrate the wall (a) to thereby enable feedingof satisfactory heating energy to the surface of inside wall (a′) facingthe space (4).

In the silicon production reactor of the present invention, theconfiguration of the raw gas supply pipe (5) is not particularlylimited, and may be cylindrical or of slit form in cross-sectional view.Further, multiple raw gas supply pipes (5) can be disposed in parallelrelationship along the longitudinal direction of the slit form incross-sectional view of the space (4) of the reaction vessel (1).Especially from the viewpoint of enhancing the uniformity of raw gasdispersed in the space (4), it is preferred that multiple cylindricalraw gas supply pipes are disposed in parallel relationship along thelongitudinal direction of the slit form. Alternatively, it is preferredthat the shape in cross-sectional view of the raw gas supply pipe besimilar to that of the space (4) of the reaction vessel (1).

Moreover, the raw gas supply pipe (5) is preferably equipped withcooling means for cooling the supply pipe for the purpose of preventingthe thermal deterioration of the supply pipe and preventing thedecomposition of various silanes as raw gas which will be describedlater. The concrete forms of cooling means (7) are not particularlylimited. For example, the cooling means (7) can be a liquid jacketsystem wherein referring to FIGS. 1 to 3, cooling is effected bydisposing such a flow channel that cooling medium such as water or heatmedium oil is fed into the interior of the raw gas supply pipe throughport (D1) and discharged therefrom through port (D2). Alternatively, thecooling means (7) can be an air cooling jacket system wherein the rawgas supply pipe is equipped with a multi-annular nozzle.

With respect to the cooling temperature for the raw gas supply pipe (5),it is satisfactory to effect cooling to such a temperature that thematerial constituting the supply pipe would not suffer seriousdeterioration. Generally, the cooling temperature is set at below theautolysis temperature of fed raw gas.

As the material of the raw gas supply pipe (5), use can be made of notonly the same materials as those of vertically extending wall (a)described later but also iron, stainless steel or the like.

One particular form of silicon production reactor according to thepresent invention will be described below with reference to FIG. 4.

With respect to other structures of the silicon production reactoraccording to the present invention, common structures such as thosedescribed in, for example, Japanese Patent Laid-open Publication No.2002-29726 can be employed without any particular limitation.

In particular, referring to FIG. 4, the reaction vessel (1) can beinstalled in sealed vessel (10) having waste gas discharge pipe (9) forwaste gas (G) connected thereto, so that not only can silicon of highpurity be obtained owing to shutting off air but also waste gas can beefficiently collected. Further, the sealed vessel (10) at its under partmay be furnished with a cooling chamber. In this cooling chamber, thereis provided a chamber for collecting silicon (15) having fallen from theopening (2). The sealed vessel (10) may be furnished with, in additionto the waste gas discharge pipe (9), cooling jacket (13) capable ofcausing cooling medium to flow from F₁ to F₂ and from F₃ to F₄ andcooling space (14) cooled by the cooling jacket (13). Further, thecooling chamber can be furnished with cooling gas supply pipe (12) tofeed cooling gas (H) for cooling obtained silicon (15). The coolingspace (14) can be of such a construction that partition board (16) isprovided therein so as to collect formed silicon (15) through take-outport (17).

Moreover, as aforementioned, when the position of the raw gas blow-offport (6) of the raw gas supply pipe (5) is equal to or below theposition of the uppermost edge of the zone wherein the surface of wall(a) facing the space (4) is heated to temperature of not lower than themelting point of silicon, for preventing the fed raw material fromleading to silicon deposition/growth in the interstice between the wall(a) and the raw gas supply pipe (5) at portion of such a low-temperatureregion that silicon is deposited in solid form, it is preferred to feeda seal gas (seal gas (C), seal gas supply pipe (8)) into thelow-temperature region. Any gas not detrimental to the production ofsilicon can be appropriately used as the seal gas. In particular, inertgases, such as argon and helium, and hydrogen can be appropriately used.When the waste gas is recycled, hydrogen is especially preferred.Moreover, the interstice between the reaction vessel (1) and the sealedvessel (10) is preferably fed with the seal gas from seal gas supplypipe (11) in order to prevent silicon deposition therein.

Furthermore, appropriately mixing a gas capable of etching silicon, suchas hydrogen chloride, with the seal gas in order to enhance the effectof seal gas provides a preferred mode.

In the present invention, the vertically extending wall (a) of thereaction vessel (1) is heated to temperature of not lower than themelting point of silicon, and the inside thereof is brought into contactwith various silanes and silicon melt. Thus, selecting a materialcapable of satisfactorily resisting these temperature condition andcontact substances is preferred from the viewpoint of performing siliconproduction stably for a prolonged period of time.

As such a material, there can be mentioned, for example, carbonmaterials such as graphite, pyrolytic carbon and acarbon-fiber-reinforced carbon composite material, and ceramic materialssuch as silicon carbide (SiC), silicon nitride (Si₃N₄), boron nitride(BN) and aluminum nitride (AlN), which materials are used independentlyor in combination.

When among these materials a carbon material is used as a base material,it is preferred that at least portion brought into contact with siliconmelt be coated with pyrolytic carbon, Si₃N₄ or SiC to preventcontamination of deposited silicon.

As the raw gas fed from the raw gas supply pipe (5) in the siliconproduction reactor of the present invention, there can be mentionedvarious silanes being used as common silicon raw gases. Specifically,there can be mentioned trichlorosilane (TCS), silicon tetrachloride(STC), monosilane, dichlorosilane, etc. Of these, monosilane and TCS arepreferred from the viewpoint that those of high purity are commerciallyavailable in large quantity. The raw gas can be used in diluted form. Asthe diluent gas, like the above seal gas, preferred use is made of gasesnot detrimental to the production of silicon. In particular, whenunreacted raw gas is recycled, it is preferred that the diluent gas behydrogen and that the ratio of raw gas dilution be such that the raw gascontent ranges from 1 to 30 mol %, especially from 3 to 20 mol %. In theuse of the diluent gas, the diluent gas may be mixed with the raw gas inadvance followed by feeding the resulting mixed gas through the raw gassupply pipe. Alternatively, another supply pipe for diluent gas may bedisposed so as to feed the diluent gas-therethrough.

In the silicon production reactor of the present invention, thetemperature employed for silicon deposition/melting on the surface ofwall (a) facing the space (4) can be appropriately determined dependingon the composition of fed raw gas, method of silicon deposition/melting,etc. From the viewpoint of stably obtaining silicon of high purity, itis preferred that using TCS as the raw gas, silicon deposition/meltingbe performed while maintaining the temperature of the wall's surface at1300 to 1700° C. In the silicon production reactor of the presentinvention, the effect of the space (4) surrounded by the wall (a) beingof slit form in cross-sectional view can be strikingly exerted when thesilicon deposition/melting is performed while maintaining the surface ofwall (a) facing the space (4) at high temperature such as 1300 to 1700°C.

In the silicon production reactor of the present invention, the pressurefor raw gas reaction, although not particularly limited as long asindustrial production can be stably performed, is generally in the rangeof atmospheric pressure to 3 MPaG, preferably atmospheric pressure to 1MPaG.

In the silicon production reactor of the present invention, although theresidence time of each gas can be appropriately regulated depending onthe reaction temperature, pressure, etc. in tubular vessel of givencapacity, the average residence time is in the range of 0.001 to 60 sec,preferably 0.01 to 10 sec, and still preferably 0.05 to 1 sec. When theresidence time is set within the above range, satisfactorily economicreactivity of raw gas can be attained.

The present invention will be described in greater detail below withreference to the following Examples, which however in no way limit thescope of the present invention.

EXAMPLE 1

Use was made of reaction vessel (1) wherein the vertically extendingwall (a) was constituted of graphite, the space (4) surrounded by thewall was of flattened form in cross-sectional view as shown in FIG. 8and the vessel had the configuration of a cylindrical form of 0.1 m SD,0.16 m LD, 15 mm thickness and 1.0 m length with opening (2) disposed atthe bottom thereof. The raw gas supply pipe (5) was constituted ofstainless steel, and the cooling means (7) had a jacket structurepermitting liquid passage. The raw gas blowoff port (6) used was of 10mm×100 mm slit form. The raw gas supply pipe (5) was disposed in thereaction vessel (1) so that the center and major diameter direction ofthe raw gas blowoff port (6) agreed with those of the flattened form ofthe space (4) and so that the height of the raw gas blowoff port (6) wassuch that the length of reaction zone (I) of FIG. 3 was 0.6 m. As theheating means (3) for heating the surface of wall (a) facing the space(4) in the reaction zone (I) to temperature of not lower than themelting point of silicon, a heating coil capable of 8 kHz high-frequencyemission (heating means) was arranged around the reaction vessel (1)from the position of 0.3 m under the upper end of wall (a) to theposition of 0.1 m under the lower end of wall (a). Furthermore, as aheat insulator, a 50 mm thick carbon fiber heat insulating material wasarranged so as to surround the reaction vessel (1) and the heating means(3) from the position of 0.2 m under the upper end of wall (a) to theposition of 0.03 m above the lower end of wall (a). The sealed vessel(10) was made of stainless steel and had an inside diameter of 1 m and alength of 1.5 m.

The surface of wall (a) facing the space (4) was heated at 1500° C. byhigh-frequency heating means (3) while cooling the raw gas supply pipe(5) and sealed vessel (10) by water flow and while effecting flow ofhydrogen gas from the seal gas supply pipe (8) and seal gas supply pipe(11) simultaneously at a rate of 5 Nm³/H.

Silicon could be stably obtained at a rate of about 1.3 kg/H by feedingtrichlorosilane and hydrogen through the raw gas supply pipe (5) atrespective rates of 35 kg/H and 100 Nm³/H. The reactivity oftrichlorosilane was about 35%. The generation of fine powder silicon wasslight and the silicon yield was enhanced. The results are summarized inTable 1.

EXAMPLE 2

Reaction was performed under the same conditions with the use of thesame reactor as in Example 1, except that the space (4) surrounded bythe vertically extending wall (a) was changed to flattened form of 0.04m SD and 0.2 m LD in cross-sectional view, that the raw gas blowoff port(6) of the raw gas supply pipe (5) was changed to 10 mm×170 mm slit formand that accordingly the configuration of high-frequency heating coil asthe heating means (3) was changed so as to surround the reaction vessel(1) with a 50 mm thick heat insulating material interposed therebetween.The results are summarized in Table 1. The generation of fine powdersilicon was extremely slight.

EXAMPLE 3

Reaction was performed under the same conditions with the use of thesame reactor as in Example 2 except for the following. The space (4)surrounded by the vertically extending wall (a) was changed to flattenedform of 0.04 m SD and 1 m LD in cross-sectional view. Accordingly, theconfiguration of high-frequency heating coil as the heating means (3)was appropriately changed. The raw gas blowoff port (6) was changed to10 mm×970 mm slit form. With respect to the sealed vessel (10), theinterior thereof was of flattened form in cross-sectional view as shownin FIG. 8, and the minor axis and major axis were changed to 0.5 m and 3m, respectively. The direction of the flattened form was the same asthat of the flattened form of the space (4).

Reaction was performed by effecting flow of hydrogen gas from the sealgas supply pipe (8) and seal gas supply pipe (11) simultaneously at arate of 25 Nm³/H and feeding trichlorosilane and hydrogen through theraw gas supply pipe (5) at respective rates of 175 kg/H and 500 Nm³/H.The results are summarized in Table 1. The generation of fine powdersilicon was extremely slight.

EXAMPLE 4

Use was made of reaction vessel (1) defined as follows. The outside wall(a) was constituted of a carbon-fiber-reinforced carbon compositematerial and had an inside diameter of 0.25 m and a thickness of 5 mm.The inside wall (a′) was constituted of a general-purpose isotropicgraphite and had an inside diameter of 0.2 m and a thickness of 15 mm.The space (4) surrounded by the outside wall (a) and inside wall (a′) inthe reaction vessel (1) was circular in cross-sectional view as shown inFIG. 6. The reaction vessel (1) had the configuration of a cylindricalform of 0.025 m SD, 0.71 m LD and 1.0 m length, having opening (2)disposed at the bottom thereof. The raw gas supply pipe (5), which wasconstituted of stainless steel and had the cooling means (7) of a jacketstructure permitting liquid passage, was arranged so as to cover theentirety of upper part of the reaction vessel (1). The upper end of theinside wall (a′) was sealed with a lid of the same material, so that theposition of the raw gas blowoff port (6) agreed with the position of theuppermost end of the wall (a) and wall (a′) As the heating means (3) forheating portion of the surfaces of the wall (a) and the wall (a′) facingthe space (4), which are capable of being contacted with raw gas, totemperature of not lower than the melting point of silicon, a heatingcoil capable of 1 kHz high-frequency emission was arranged around theoutside wall (a) from the position of 0.15 m under the upper end of wall(a) to the position of 0.1 m under the lower end of wall (a).Furthermore, a 50 mm thick carbon fiber heat insulating material wasarranged between the heating coil and the outside wall (a) from theuppermost end of outside wall (a) to the position of 0.03 m above thelower end of outside wall (a) as well as over the upper end part lidsealing the inside wall (a′). The sealed vessel (10) was made ofstainless steel, having an inside diameter of 1 m and a length of 1.5 m.

The surfaces of the wall (a) and the wall (a′) facing the space (4) wereheated at 1300° to 1400° C. by high-frequency heating means (3) whilecooling the raw gas supply pipe (5) and sealed vessel (10) by waterflow.

Reaction was performed by feeding trichlorosilane and hydrogen throughthe raw gas supply pipe (5) at respective rates of 175 kg/H and 500Nm³/H. The operation of feeding the raw gas at the above feeding ratefor 2 hr and thereafter reducing the feeding rate of raw gas to ⅓ for 15min was repeated. At the time of reduction of gas feeding rate, siliconwas melted and fell. The results are summarized in Table 1. Thegeneration of fine powder silicon was extremely slight.

COMPARATIVE EXAMPLE 1

Reaction was performed under the same conditions with the use of thesame reactor as in Example 1 except for the following. The space (4)surrounded by the vertically extending wall (a) was of circular form of0.15 m inside diameter in cross-sectional view. The length of thereaction zone (I) was 0.6 m. The raw gas blowoff port was also ofcircular form of 40 mm. Further, accordingly, the configuration ofhigh-frequency heating coil as the heating means (3) was changed so asto surround the reaction vessel with a 50 mm thick heat insulatingmaterial interposed therebetween. The results are summarized in Table 1.The generation of fine powder silicon abounded to some extent.

COMPARATIVE EXAMPLE 2

Reaction was performed under the same conditions with the use of thesame reactor as in Example 3 except for the following. The space (4)surrounded by the vertically extending wall (a) was of circular form of0.23 m inside diameter in cross-sectional view. The length of thereaction zone (I) was 0.6 m. The raw gas blowoff port was also ofcircular form of 60 mm. Further, accordingly, the configuration ofhigh-frequency heating coil as the heating means (3) was changed so asto surround the reaction vessel with a 50 mm thick heat insulatingmaterial interposed therebetween. The results are summarized in Table 1.The generation of fine powder silicon abounded to some extent. TABLE 1Length Quantity of Reaction Residence of reaction surface Reaction Rateof time of Reactivity Silicon silicon SD LD zone I area* volume**feed*** gas of TCS yield**** produced [m] [m] LD/SD [m] [m²] [m³][Nm³/H] [S] [%] [mol %] [kg/H] Example 1 0.10 0.16 1.6 0.6 0.26 0.008106 0.28 35 51 0.9 Example 2 0.04 0.2 5 0.6 0.27 0.005 106 0.16 55 522.1 Example 3 0.04 1.00 25 0.6 1.23 0.024 529 0.16 53 53 10 Example 40.025 0.71 28.4 0.85 1.20 0.015 529 0.10 45 60 9.8 Comp. Ex. 1 0.15 0.151 0.6 0.28 0.011 106 0.36 22 48 0.8 Comp. Ex. 2 0.23 0.23 1 0.6 0.430.025 529 0.17 20 48 0.7*Inside surface area of vertically extending wall within reaction zone I**Vol. of space surrounded by vertically extending wall within reactionzone I***Rate of feed of total of TCS and hydrogen****Ratio of TCS converted into silicon to reacted TCS

Referring to Table 1, it is apparent from comparison between Examples1-2 and Comparative Example 1 that when the surface areas of portionassociated with silicon formation in the reaction vessel are nearlyequal to each other, not only is the reactivity of raw gas high but alsothe unfavorable generation of fine powder can be reduced to result inhigh silicon yield despite the short residence time of raw gas inExamples 1-2.

Further, it is apparent from comparison between Example 3 andComparative Example 2 that when in the reaction vessel not only thevolumes but also the gas residence times are nearly equal to each other,the reactivity of raw gas is so high that the quantity of siliconproduced can be increased to a large extent in Example 3.

The use of the silicon production reactor of the present invention, evenwhen scaleup of the reaction vessel is effected, has realizedmaintaining of a high reactivity of raw gas and strikingly efficientincreasing of a quantity of silicon produced.

EFFECT OF THE INVENTION

As apparent from the above description, the silicon production reactorof the present invention, even when scale-up of the reactor is effected,has realized an enhancement of raw gas reactivity and further amaintaining of high silicon yield through suppression of by-productformation with the result that the continuous production efficiency hasbeen enhanced to a striking extent for a prolonged period of time.Moreover, the silicon production reactor has realized an effectiveprevention of radiant heat loss at both ends of the space surrounded bythe vertically extending wall.

1. A silicon production reactor comprising a reaction vessel and heatingmeans, said reaction vessel comprising a vertically extending wall and aspace surrounded by the wall, said heating means being capable ofheating at least a part, including lower end portion, of the wall'ssurface facing the space to a temperature of not lower than the meltingpoint of silicon, said silicon production reactor being adapted to flowraw gas for silicon deposition from an upper part of the space of thereaction vessel toward a lower part thereof, characterized in that thespace of the reaction vessel is of slit form in cross-sectional view. 2.The silicon production reactor as claimed in claim 1, wherein the slitform has a ratio (LD/SD) of length (LD) to width (SD) of 1.5 or more. 3.The silicon production reactor as claimed in claim 1, wherein the width(SD) of the slit form is 0.1 m or less.
 4. The silicon productionreactor as claimed in claim 1, wherein the vertically extending wall isconstituted of a material capable of being heated by high-frequencyapplication, wherein a high-frequency generation coil is arranged aroundthe vertically extending wall so as to enable heating of the verticallyextending wall.
 5. The silicon production reactor as claimed in claim 2,wherein the width (SD) of the slit form is 0.1 m or less.
 6. The siliconproduction reactor as claimed in claim 2, wherein the verticallyextending wall is constituted of a material capable of being heated byhigh-frequency application, wherein a high-frequency generation coil isarranged around the vertically extending wall so as to enable heating ofthe vertically extending wall.
 7. The silicon production reactor asclaimed in claim 3, wherein the vertically extending wall is constitutedof a material capable of being heated by high-frequency application,wherein a high-frequency generation coil is arranged around thevertically extending wall so as to enable heating of the verticallyextending wall.